Tandem variable resistor control



Jan. 3, 1950 w. H. BUDD ET AL TANDEM VARIABLE-RESISTOR con'raon Filed Sept. 24, 1949 Wilbert HBg/dd Nprvm .fiArzsman Rabert R- Thumpsan Q t faientedr-Jan. 3 .1950: 7

TANDEM VARIABLE RESISTOR CONTROL Wilbert H. Budd, Mervin B. Arlsman, and Robert R. Thompson, Elkhart, Ind., assignors to Chicago Telephone Supply Corporation, Elisha-rt,

Ind., a corporation of Indiana Application September 24, 1949, Serial No. 117,703

Claims. (Cl. 201-55) This invention relates to electrical control devices and refers particularly to tandem variable resistor controls of the type used in radio and television equipment.

In such tandem controls the two control units are generally alike except that the rear unit often has a switch mcunted'thereon. Each of the units comprises the customary control instrumentalities including a resistance element mounted on a base of insulating material, a control shaft rotat able in the base and a contactor carried by the shaft and adapted to traverse the resistance element as the shaft is turned.

A cup-shaped metal casing is secured to the base over the control instrumentalities so as to enact with the base and provide an enclosing housing therefor. The necessary terminals for the resistance element and contactor are mounted upon the base with portions thereof exposed on the outer face of the base.

In their tandem relationship both control units face in the same direction. This requires the control shaft of the rear unit to be received in and project through the shaft of the front unit.

Since the contactor of each unit engages its resistance element under spring tension, means must be provided to hold the shaft of each unit against inward displacement. In the case of the front unit the entire rotatable assembly is generally supported against inward thrust by having a portion thereof bear on the end wall of its casing; but for the rear unit this manner of supporting the shaft is not feasible. This follows from the fact that the rear unit ordinarily has a switch mounted thereon to be actuated by rotation of the shaft of the rear unit, the driving connection to the switch passing through a relatively large hole in the casing end wall of. the rear unit. Hence, it has been the practice to employ a C-washer fitted to the shaft of the rear unit and bearing against an insulated spacer overlying the base through which the shaft protrudes.

While this construction generally provedfairly satisfactory there was always the dangerfof inward endwise forces accidentally being applied to the protruding end of the inner shaft, i. e. the shaft of the rear unit, and disrupting the instrumentalities thereof since the stress resulting from such inward forces was carried by the base.

In recognition of this objection it isthe purpose of this invention to provide a simple but highly effective manner of relieving the base of the rear unit of any stress resulting from inward endwise forces to which its shaft might be subjected.

' units of a tandem variable resistor.

Another object of this invention is to utilize the same means by which these stresses are kept from being imposed upon the base and the control instrumentalitles mounted thereon to also'space the two units from each other and thus obviate the insulated spacing washer heretofore used.

More specifically it is an object of this invention to provide in a tandem control of the character described a combination c-washer and spacer plate which is simply and cheaply formed as a sheet metal stamping and so shaped as to have interiltting engagement with the annular groove in the control shaft, and when in position provides adequate electrical clearance between the terminals of the rear unit and all grounded portions of thecontrol device.

With the above and other objects in view, which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the rinciples thereof, and in which:

Figure 1 is a top view of a tandem control device embodying this invention;

Figure 2 is a side view of the control device with the base and control instrumentalities of the front section removed and with portions broken away and in section;

Figure 3 is a perspective view of the rear control unit alone showing the combination c-washer and spacer plate of this invention in position thereon: and

Figure 4 is a perspective view of the combination O-washer and spacer plate per se.

Referring now particularly to the drawing the numerals 4 and 5 designate the front and rear As brought out hereinbefore, each of these units has a base of insulating material, and these bases, though identical, are for convenience of description designated 6 and 1. The inner face of each base has an arcuate resistance element 8 mounted thereon to be traversed by a contactor 9. The contactor of the front unit 4 is mounted upon and controlled by a hollow shaft III which passes through the base 8 and is ioumalled in a mounting bushin: II secured to the front face of the device and aware the front end of the hollow outer shaft III to enable each shaft to have its own control knob secured thereto.

A stamped cup-shaped metal casing I3 is seated 'upon the base of each control unit to enclose the control lnstrumentalitles thereof, and attention is directed to the fact that the base in each instance has portions resting ,upon the edge of the casing. As is customary the edges of the casing have attaching tangs l4 extended therefrom, those of the front casing being bent over the mounting plate of the bushing II and those of the rear casing passing through slots I5 in the back wall of the front unit casing to be clinched thereover and hold the two units together. It is to be noted that this arrangement ties the two casings to each other and to the mounting bushing H.

The base of each unit has a terminal carrying portion [6 extending therefrom through an appropriate opening in the side wall of the casing and the necessary terminals ll, i8 and IQ for the two ends of the resistance element and the contactor are mounted upon this base portion I6. The manner in which the terminals are mounted exposes parts thereof on the outer face of the base as clearly shown so that the two units must be spaced apart to maintain electrical clearance between the exposed portions of the electrical terminals and the back wall of the casing of the front unit. This necessary spacing is conveniently achieved by a combination C-washer and spacer plate which is stamped from stiif sheet metal.

The spacer plate 20 has a deep notch 2i opening to one side edge thereof to embrace the shaft i2, and the bottom of this notch is reduced in size to have snug interfltting engagement with an annular groove 22 in the shaft i 0.

At diametrically opposite points the spacer plate has outwardly projecting marginal portions or ears 23 which extend far enough to overlie the adjacent edge portions of the casing. Hence, any stress resulting from inward endwise force applied to the shaft l2 will be carried by the spacer plate into the casing walls, thereby precluding the possibility of such stress being imposed upon the control instrumentalities within the casing. It is, of course, to be understood that portions of the base 1 underlie the cars 23- but these underlying portions of the base are merely placed in compression by inward endwise forces on the shaft and hence impose no strains upon the control instrumentalities.

When the two units are assembled the spacer plate 20 is clamped between them and serves to provide the necessary electrical clearance between the terminals of the rear unit and the adjacent back wall of the front unit casing, and to this end the spacer plate is so shaped that although it overlies a major portion of the base 1 adequate electrical clearance is maintained between it and the terminals. In this connection it is to be noted that the exposed portion of the center terminal I! is received in the wide outer portion of the notch 2|.

Shifting of the plate 20 on the base 1 is precluded 4 by a lug 2| struck from'the plate and engaging in a hole 25 in the base.

From the foregoing description taken in connectlon with the accompanying drawing it will be readily apparent to those skilled in this art that the novel combination O-washer and spacer plate of this lnveintion effects a definite improvement in tandem resistor controls, and has the added advantage of reducing the cost of the control device since by a simple stamping two previously necessary parts are obviated.

What we claim as our invention is:

1. A tandem variable electrical control device having front and rear control units each of which has its instrumentalities encased within a cupshaped metal casing closed by a base member of insulating material upon which the terminals of the unit are mounted with parts thereof exposed on the exterior of the base member, said units facing in the same direction so that the base member of the rear unit and the bottom wall of the metal casing of the front unit are adjacent to each other, each unit having a rotatable control shaft protruding through the base member thereof the shaft for the front unit being hollow and receiving the shaft of the rear unit therein, characterized by the provision of a stiff metal spacer plate between the two units; fastening means connecting the casings of the two units and thus holding the units together with the spacer plate clamped therebetween; the spacer plate being shaped to afford adequate electrical clearance between it and the adjacent turminals of the rear unit and spacing the back wall of the front unit from said terminals: and the spacer plate having a notch therein which embraces the shaft of the rear unit and has interfitting engagement with an annular groove in said shaft whereby the spacer plate is adapted to react against endwise forces imposed upon said shaft in a rearward direction and carries the stress resulting from such endwise forces to the side wall of the rear unit casing through the intervening base member.

2. The tandem variable electrical control device of claim 1 further characterized by the provision of marginal portions on the spacer plate overlying the adjacent edge portions of the rear casing so that the only stress imposed upon the intervening base member as a result of rearward endwise forces on the shaft of the rear unit is that of direct compression of those portions thereof lying between said marginal portions of the spacer plate and the edge of the casing.

3. The tandem variable electrical control device of claim 1 further characterized by the fact that the notch in the spacer plate provides electrical clearance between the plate and one of the terminals; and means restraining the spacer plate against shifting on the base of the rear unit.

4. In a variable resistor: a stationary resistance element; a base of insulating material upon which the resistance element is mounted; a rotatable shaft rotatable in the base; a contactor connected with the shaft to be driven thereby and adapted to traverse the resistance element as the shaft is turned; a cup-shaped casing disposed over the resistance element and contactor and closed by the base with portions of the base resting on the edge of the cup-shaped casing so that the base coacts with the casing to enclose the operating instrumentalities of the resistor; a still metal plate overlying the exterior of the base, said plate having a notch therein which such inward forces on the shaft; and means on the casing for mounting the entire unit on a supportingwall with the plate clamped between the supporting wall and the base.

5. The electrical control device of claim 4 further characterized by the fact that the rresist- 15 has interfltting engage- 6 an ce element and contactor have terminals mounted on the base with portions thereof exposed on the outer face of the base, the plate being shaped to have suflicient electrical clearance from said terminals; and means for holding the plate against shifting 0n the base so that by virtue of its interposition between the supporting wall and the base said plate serves to electrically space the terminals from the supporting wall.

v WILBERT H. BUDD.

MERVIN B. ARISMAN. ROBERT R. THOMPSON.

No references'cited. 

